222 research outputs found
Structure of Extremely Nanosized and Confined In-O Species in Ordered Porous Materials
Perturbed-angular correlation, x-ray absorption, and small-angle x-ray
scattering spectroscopies were suitably combined to elucidate the local
structure of highly diluted and dispersed InOx species confined in porous of
ZSM5 zeolite. These novel approach allow us to determined the structure of
extremely nanosized In-O species exchanged inside the 10-atom-ring channel of
the zeolite, and to quantify the amount of In2O3 crystallites deposited onto
the external zeolite surface.Comment: 4 pages, 5 postscript figures, REVTEX4, published in Physical Review
Letter
Cationic exchange in nanosized ZnFe2O4 spinel revealed by experimental and simulated near-edge absorption structure
The non-equilibrium cation site occupancy in nanosized zinc ferrites (6-13
nm) with different degree of inversion (0.2 to 0.4) was investigated using Fe
and Zn K-edge x-ray absorption spectroscopy XANES and EXAFS, and magnetic
measurements. The very good agreement between experimental and ab-initio
calculations on the Zn K-edge XANES region clearly show the large
Zn2+(A)--Zn2+[B] transference that takes place in addition to the
well-identified Fe3+[B]--Fe3+(A) one, without altering the long-range
structural order. XANES spectra features as a function of the spinel inversion
were shown to depend on the configuration of the ligand shells surrounding the
absorbing atom. This XANES approach provides a direct way to sense cationic
inversion in these spinel compounds. We also demonstrated that a mechanical
crystallization takes place on nanocrystalline spinel that causes an increase
of both grain and magnetic sizes and, simultaneously, generates a significant
augment of the inversion.Comment: 5 pages, 5 eps figures, uses revtex4, corrected table
Una Experiencia de Prevención del Acoso Entre Pares en Niños Escolarizados
En el presente trabajo se presenta la experiencia de capacitación con docentes y directivos en relación a la prevención del acoso entre pares (presencial y virtual) en niños de Escuelas Municipales de la ciudad de Córdoba. Se adopta el enfoque de educación en habilidades para la vida como estrategia para la construcción de una convivencia saludable en el ámbito escolar, en consonancia con los lineamientos formulados por la Organización Panamericana de la Salud (2001), la cual recomienda que los programas escolares integren al currículo los conocimientos, valores y habilidades necesarias para el desarrollo de estilos de vida saludable. Sensibilizar y concienciar a los docentes sobre la necesidad de intervenir y desarrollar actuaciones para fortalecer habilidades interpersonales y de la comunicación como forma de reducción y prevención del acoso entre pares. La experiencia se abordó desde la metodología de Investigación Acción Participativa. Se desarrollaron 4 encuentros con modalidad de jornada taller de 4 horas cada uno. Participaron 45 docentes y 60 directivos. Los participantes discriminan conductas de riesgos en relación al acoso entre pares de aquellas acciones que favorecerían la salud y convivencia; destacaron la importancia de favorecer la comunicación; proponen el trabajo cooperativo, fomentando la solidaridad; reconocen la problemática del acoso entre pares y su incidencia en edades tempranas. El trabajo demuestra que el docente, en la medida que fortalece en los alumnos diferentes habilidades interpersonales y de la comunicación, potencia la construcción de vínculos solidarios orientados a la convivencia saludable a nivel escolar, familiar y comunitario
Propuesta de modelo integral de evaluación sostenible de la vivienda social en México
ResumenDebido al gran impacto de la industria de la construcción en el medio ambiente, la tendencia de la construcción sustentable a nivel mundial es una gran necesidad. La industria de la construcción es la principal actividad humana consumidora de recursos naturales por lo que se han creado herramientas que certifican el nivel de sustentabilidad e impacto ambiental de los edificios. En México aún no se ha desarrollado alguna metodología que evalue el grado de sustentabilidad de vivienda, por lo que se ha visto la necesidad de implementar modelos extranjeros, diseñados por otros países y para otros contextos, no viables de aplicar debido a las diferencias de los sistemas constructivos. El trabajo de investigación tiene como objetivo producir un modelo de evaluación de sustentabilidad en la vivienda social, creado en base a las características y sistemas constructivos preponderantes en el contexto local. Se analizaron los modelos de sustentabilidad más conocidos a nivel mundial (BREEAM, CASBEE, LEED y VERDE) en las etapas del ciclo de vida del edificio que ellos evalúan y a partir de esta revisión se diseñó una metodología de evaluación para la vivienda social sustentable en el país; la cual se aplicó en un caso estudio local y arrojó como resultado la gran necesidad de reforzar las prácticas sustentables locales ya que el nivel de cumplimiento de los criterios definidos fue tan sólo un 52% de su totalidad
Spontaneous oxidation of disordered fcc FePt nanoparticles
In this work we present new results on spontaneous oxidation of disordered fcc FePt nanoparticles. The "as-made" oleic acid and oleylamine coated FePt nanoparticles of average size 4 nm synthesized by a high-boiling coordinating solvent method were exposed to air over a period of days and characterized structurally and magnetically by means of different techniques such as XANES, XPS, EXAFS, and SQUID magnetometry. The "as-made" FePt nanoparticles stabilize in the disordered fcc structure and have a very low magnetic saturation (M(s)=11 emu/g) and a huge coercive field (H_(c)=1800 Oe) compared to the low temperature bulk values of the disordered fcc FePt. We observed that the coercive field and the magnetic saturation change with the time the sample is exposed to air and these changes are associated with the oxidation or passivation of the nanoparticle surface that gives place to a core-shell structure. Indeed, the study on the electronic properties of the nanoparticles confirms the magnetic results and indicates that when the nanoparticles are exposed to air, changes in the oxidation state of both Fe and Pt occur, the oxidation state of Fe coming close to hematite. The formation of hematite tends to soften the "as-made" FePt nanoparticles as observed by the reduction of the coercive field to almost one third of the original value. Although the hematite softens the FePt nanoparticles, there is an exchange coupling at the interface of the core-shell characterized by the increase of the coercive field from 300 to 900 Oe when the sample is cooled in an applied field of 50 kOe
Effect of operating conditions on performance of domestic heating systems with heat pumps and fuel cell micro-cogeneration
Wrapped branes with fluxes in 8d gauged supergravity
We study the gravity dual of several wrapped D-brane configurations in
presence of 4-form RR fluxes partially piercing the unwrapped directions. We
present a systematic approach to obtain these solutions from those without
fluxes. We use D=8 gauged supergravity as a starting point to build up these
solutions. The configurations include (smeared) M2-branes at the tip of a G_2
cone on S^3 x S^3, D2-D6 branes with the latter wrapping a special Lagrangian
3-cycle of the complex deformed conifold and an holomorphic sphere in its
cotangent bundle T^*S^2, D3-branes at the tip of the generalized resolved
conifold, and others obtained by means of T duality and KK reduction. We
elaborate on the corresponding N=1 and N=2 field theories in 2+1 dimensions.Comment: 32 pages, LateX, v2: minor changes, reference added, v3: section
3.5.2 improve
Conductivity of underdoped YBa2Cu3O7-d : evidence for incoherent pair correlations in the pseudogap regime
Conductivity due to superconducting fluctuations studied in optimally doped
YBa2Cu3O7-d films displays a stronger decay law in temperature than explainable
by theory. A formula is proposed, which fits the data very well with two
superconductive parameters, Tc and the coherence length ksi_c0, and an energy
scale Delta*. This is also valid in underdoped materials and enables to
describe the conductivity up to 300 K with a single-particle excitations
channel in parallel with a channel whose contribution is controlled by ksi_c0,
Tc and Delta*.
This allows to address the nature of the pseudogap in favour of incoherent
pairing.Comment: 14 pages, 4 figures, 1 tabl
Structure of extremely nanosized and confined In-O species in ordered porous materials
Perturbed-angular correlation, x-ray absorption, and small-angle x-ray scattering spectroscopies were suitably combined to elucidate the local structure of highly diluted and dispersed InOₓ species confined in the porousof the ZSM5 zeolite. This novel approach allow us to determined the structure of extremely nanosized In-O species exchanged inside the 10-atom-ring channel of the zeolite, and to quantify the amount of In₂O₃ crystallites deposited onto the external zeolite surface.Facultad de Ciencias Exacta
Supersymmetric Intersections of M-branes and pp-waves
We study supersymmetric intersections of M2 and M5 branes with different
pp-waves of M-theory. We consider first M-brane probes in the background of
pp-waves and determine under which conditions the embedding is supersymmetric.
We particularize our formalism to the case of pp-waves with 32, 24 and 20
supersymmetries. We also construct supergravity solutions for the brane-wave
system. Generically these solutions are delocalised along some directions
transverse to the brane and preserve the same number of supersymmetries as in
the brane probe approach.Comment: 41 pages, LaTeX; v2 references adde
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